Introduction

This article will look at the work carried out by the company's team in analyzing an overhead crane. During the study, activities included visual inspection, non-destructive testing, extensometry, structural analysis and analysis of the repowering of the asset.

The crane in question is made up of two outer main beams, two inner main beams, two interconnecting beams, a main lifting carriage, an auxiliary lifting carriage and the travel system. The asset's main function is to transport and tip pig iron ladles for the steel production process. Figure 1 shows a general view of the bridge.

Figure 1: General view photograph of the crane. [1]

Figure 2 shows the views of the technical drawing of the asset with an indication of the systems that make up the machine.

Figure 2: Crane subdivision. [1]

Field Services

The services carried out in the field were aimed at inspecting the crane's Structural Integrity , identifying points of non-conformity in order to indicate possible measures needed to adapt the equipment to safe operation. To this end, the condition of the structures was checked using visual inspection methods, non-destructive testing using ultrasound and liquid penetrant.

• Visual inspection

A visual inspection was carried out to check the general condition of the equipment, looking for corrosion spots in the structure. The main welded joints were also inspected and possible deformed profiles and plates and design modifications were assessed.

During this inspection some points of non-compliance were found, some of which can be seen below.

Figure 3 shows a weld at the head of the auxiliary beam in which the weld bead was not completely filled, while Figure 4 identifies a deformation in the main car stop.

Figure 3: Weld with lack of fusion detected at the head of the auxiliary beam. [1]

Figure 4: Deformation at the main carriage stop. [1]

Elements within the expected conformities were also found and recorded during the visual inspection. Figure 5 shows the wheel of the auxiliary trolley.

Figure 5: Position of the trolley wheel. [1]

Once the visual inspections had been completed, Kot indicated that the best course of action in the case of the deviations observed would be to wait for the structural analysis Technical Report to verify the dimensioning of the elements. For the elements found to be within the expected parameters, a periodic inspection plan was indicated.

• Extensometry

The extensometry analysis was carried out in several stages of commanded operation in which it was possible to evaluate the deformation at specific points in the structure. During the test, the crane was moved several times in order to calibrate the computer model with a standard load of known mass. 

Figure 6 shows the graph containing the results obtained during extensometry. The information will be used in the structural analysis by finite element of the crane to calibrate the computer model.

Figure 6: Results obtained during extensometry. [1]

• Non-destructive testing

Non-destructive liquid penetrant and ultrasound tests were carried out on the existing welds. No points of non-conformity were found.

Structural analysis

In view of the non-conformities found, Kot carried out a structural analysis of the bridge, with the aim of identifying points of concern in the structure and assessing possible causes. Some of the objectives of the structural assessment are listed below:

• Static structural analysis;
• Fatigue analysis;
• Buckling analysis;
• Link analysis.

For the structural analysis of the crane, finite element models of the structure were created using specific software. The finite element can be seen in Figure 7 and Figure 8.

Figure 7: Finite element model of the crane. [1]

Figure 8: Finite element model of the main elevation beam. [1]

The results found during the structural simulations are summarized below:

• Static structural analysis: 

Points were found where the utilization rate is higher than the rate allowed by the standard.

• Fatigue analysis: 

Points were found where the utilization rate is higher than the rate allowed by the standard.

• Buckling analysis: 

No points of non-compliance were found.

• Link analysis: 

Points were found where the utilization rate is higher than the rate allowed by the standard.

Figure 9 shows one of the results found during the static analysis of the equipment.

Figure 9: Utilization rates in the main car manual. [1]

The finite element model developed by Kot was validated by comparing the deformations measured during extensometry on the crane with the deformations found in the model for similar loading conditions; the results of this comparison can be seen in Figure 10.

Figure 10: Deformations obtained from extensometry and the model. [1]

Comparing the data, it was observed that the deformations present in the bridge structure are consistent with the deformations found in the model and are sufficient to guarantee that the results obtained in the model are valid for the real bridge structure. As a result, the computational model of the bridge was considered valid.

Repowering analysis

This part of the study was responsible for verifying the feasibility of repowering the capacity of the bridge's main lift to increase its capacity. To do this, it was necessary to carry out a structural and mechanical assessment of the asset, taking into account the new loads desired by the client company.

After carrying out the analyses, Kot found no restrictions on repowering the crane, provided that the reinforcements indicated were installed for the repowered condition.

Conclusion

At the end of the analysis, due to the non-conformities found in the structural analysis of the crane, concepts were presented for the changes or reinforcements needed to bring the structure into line with the criteria established in the standard.

Field work is often crucial to the development of a complete study. Identifying points of non-compliance can prevent production stoppages and even accidents. When combined with computer analysis, it is possible to have a complete understanding of the working context of an asset, validating computer models and gathering information that often goes unnoticed.

Kot Engenharia has employees able to work in the field, carrying out visual inspections, non-destructive testing and data collection. Our team can also carry out various computer analyses. Contact our team for more information!

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